Many internal combustion engines utilize Gasoline Direct Injection (GDI) to increase the power efficiency and range over which the fuel can be delivered to the cylinder. One potential issue with GDI is that under lower fuel pressures the fuel may not sufficiently mix with the air in the cylinder. Insufficient mixing may decrease engine power and efficiency, and increase emissions, at least under some conditions. For example, during cold engine starts, and before the catalytic converter is activated, insufficient mixing as a result of lower fuel pressure may exacerbate cold start emissions.
In one example, a fuel delivery system includes a lower pressure fuel pump and a high pressure fuel pump in combination to achieve a higher fuel pressure. However, at startup the two-pump system may require a longer duration to pump fuel at the higher fuel pressure, which may result in engine miss-starts. Further, the slow response time of the fuel pumps may allow for pulsations in fuel pressure to cause inaccurate amounts of fuel to be injected for combustion. Moreover, the consistently higher fuel pressure may cause increased wear on components of the fuel delivery system.
One approach to provide variable fuel pressure during vehicle operation may include utilizing a method for operating an engine direct injection fuel system including a mechanical fuel pressure regulator that has a spring actuatable by an electric motor. The method includes adjusting a preload of the spring by operating the electric motor to adjust a set-point fuel pressure from a first set-point fuel pressure to a second set-point fuel pressure in response to an operating condition, and maintaining the preload of the spring mechanically when the electric motor is not operating.
By implementing a mechanical fuel pressure regulator having a spring preload that may be mechanically maintained and adjusted via operation of an electric motor, fuel pressure pulsations may be compensated for quickly and a set-point fuel pressure may be adjusted dynamically during various operating conditions. In this way, fuel pressure may be regulated consistently, which in turn may improve fuel injection accuracy. Moreover, the electric motor of the fuel pressure regulator may be operated to adjust the spring preload and then the adjusted spring preload may be maintained mechanically. By only operating the electric motor to make spring preload adjustments energy consumption may be reduced and durability may be improved.
Another approach to provide temporarily increased fuel pressure for engine starting may be a method for operating a fuel system of a vehicle utilizing gasoline direct injection for an internal combustion engine, the fuel system including at least one fuel pump, a fuel pressure regulator fluidly coupled to the at the least one fuel pump, the mechanical fuel pressure regulator having a spring actuatable by an electric motor, the method comprising: increasing a preload of the spring of the mechanical fuel pressure regulator by operating the electric motor to set a first set-point fuel pressure in response to an engine shutdown condition; activating the at least one fuel pump to increase a fuel pressure to the first set-point fuel pressure in response to an engine start condition following the engine shutdown condition; and decreasing the preload of the spring of the mechanical fuel pressure regulator by operating the electric motor to adjust the first set-point fuel pressure to a second set-point fuel pressure that is lower than the first set-point fuel pressure in response to exceeding a threshold after engine start.
By increasing the spring preload and maintaining it in preparation for the next engine start, the set-point fuel pressure may already be established and activation of the low pressure pump flow may be dedicated to replenishing the high pressure pump immediately instead of waiting for set-point fuel pressure adjustment at startup (e.g., key-on) for quicker fueling and engine starting. This approach may provide faster closed loop fuel pressure control during startup and during low engine fuel consumption conditions. Moreover, by utilizing a preload of a spring in the fuel pressure regulator to adjust fuel pressure, the fuel pressure set-point may be decreased after startup to reduce wear on fuel delivery system components. In this way, the operational lifetime of the fuel delivery system may be increased. The above described approaches may provide high control accuracy to dynamically adjust the set-point fuel pressure whether it be to dampen pressure pulsations during vehicle operation or to enable quicker and more robust engine starts.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.